Triglyceride-based base oil for hydraulic oils

ABSTRACT

Hydraulic oils containing a biodegradable base oil comprising either 
     a) the product of the ethoxylation and/or propoxylation of glycerol with from about 0.5 to about 3 moles of ethylene oxide and/or propylene oxide and subsequent esterification with a saturated or unsaturated C 6-24  fatty acid, or mixtures thereof; or 
     b) the product of the insertion of from about 0.5 to about 3 moles of EO and/or PO into a natural oil or fat other than castor oil.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a biodegradable triglyceride-based base oil,to its production and to hydraulic oils containing this base oil.

2. Statement of Related Art

In the past, most hydraulic oils were produced from mineral oil. Thesame is still true today. In applications where the escape of oil intothe environment has to be accepted as a possibility, for example throughunavoidable leakages, there is an increasing demand for hydraulic oilswhich contain environmentally friendly ester oils, particularly thosebased on rapeseed oil and/or soybean oil, as their oil base. Typicalapplications of the type in question include the machinery and toolsused in forestry, agriculture, building and the like. These applicationsrequire the use of hydraulic oils belonging to water hazard class 0-1.Ester-based hydraulic oils are capable of meeting these requirements.

However, ester oils of the above-mentioned type essential for practicalapplication, i.e. oils based on purified rapeseed oils and/or soybeanoils, more particularly those freed from aminopectins and otherslime-forming substances, have two distinct weaknesses in terms ofpractical application, namely:

Ester oils based on polyunsaturated fatty acid systems tend to thickenrapidly, even at only moderately elevated operating temperatures, forexample in the range from 50° to 80° C. The reason for this is thereadiness of the olefinic double bonds of the ester-forming acids of theoil type in question to enter into viscosity-increasing reactions in thepresence of atmospheric oxygen. Although it is known in principle thatsuch unwanted increases in viscosity in hydraulic oils can be avoided bythe addition of antioxidants, it has been found that the antioxidantshitherto preferably used in hydraulic oils based on mineral oils performunsatisfactorily in ester oils of the type in question.

Another important limitation of hydraulic oils based on theenvironmentally friendly ester oils mentioned is their inadequatestability at low temperatures. For example, purified rapeseed oil has asolidification point or pour point of -16° C. Even before thesolidification point is reached, a remarkable increase in viscosityoccurs with decreasing temperatures. The comparatively high pour pointof rapeseed oil, for example in winter, poses considerable problems forthe practical application of the hydraulic oils at low ambienttemperatures. These problems can of course be made considerably worse inpractice if, at the same time, the considerable increase in the pourpoint of the hydraulic oil is initiated by oxidative thickening of theabove-mentioned ester oil. The addition of pour point depressants doesnot solve the technical problem involved. It is known that the effect ofpour point depressants disappears after prolonged presence in the oil tobe treated.

DE-A-39 27 155 describes an environmentally friendly base oil based onnatural substances for the formulation of hydraulic oils containing arapeseed oil and/or soybean oil as the main oil component, speciallyselected antioxidants and a quantity equal to the main oil component ofesters of trimethylol ethane, trimethylol propane and/or neopentylalcohol with C₅₋₁₀ monocarboxylic acids or at least partly unsaturatedfatty acids based on rapeseed oil, soybean oil or sunflower oil.

DESCRIPTION OF THE INVENTION

The problem addressed by the present invention was to provide base oilsfor the formulation of hydraulic oils which would show highlow-temperature stability without any need for the addition of pourpoint depressants or synthetic esters.

According to the invention, the problem stated above has been solved bytriglyceride-based base oils obtainable by

a) ethoxylation and/or propoxylation of glycerol with 0.5 to 3 moles ofethylene oxide (EO) and/or propylene oxide (PO) and subsequentesterification with saturated and/or unsaturated C₆₋₂₄ fatty acids fromnatural sources or mixtures thereof by methods known per se or

b) insertion of 0.5 to 3 moles of EO and/or PO into natural oils or fatsby methods known per se.

Preferably 0.5 to 2 moles and, more preferably, 0.5 to 1 mole of EOand/or PO is/are used for the ethoxylation and/or propoxylation ofglycerol.

Preferably 0.5 to 2 moles and, more preferably, 0.5 to 1 mole of EOand/or PO is/are preferably used for the insertion of EO and/or PO intothe natural oils or fats.

Suitable fatty acid components for the esterification of the reactionproducts of EO and/or PO with glycerol are unsaturated or saturatedC₆₋₂₄ fatty acids from natural sources.

Particularly preferred saturated fatty acids are hexanoic acid (caproicacid), octanoic acid (caprylic acid), decanoic acid (capric acid),dodecanoic acid (lauric acid), tetradecanoic acid (myristic acid),hexadecanoic acid (palmitic acid), octadecanoic acid (stearic acid),eicosanoic acid (arachic acid), docosanoic acid (behenic acid) ortetracosanoic acid (lignoceric acid).

Particularly preferred unsaturated fatty acids are tetradecenoic acid(myristoleic acid), hexadecenoic acid (palmitoleic acid), octadecenoicacid (oleic acid), eicosenoic acid (gadoleic acid), docosenoic acid(erucic acid), 12-hydroxyoctadecenoic acid (ricinoleic acid),octadecadienoic acid (linoleic acid), octadecatrienoic acid (linolenicacid), eicosatetraenoic acid (arachidonic acid) or docosapentaenoic acid(clupanodonic acid).

Coconut oil, palm kernel oil, palm oil, peanut oil, cotton oil, soybeanoil, sunflower oil, rapeseed oil rich or poor in erucic acid, castoroil, tallow and fish oil are preferably used for the insertion of EOand/or PO into the natural oils or fats.

The process for the ethoxylation and/or propoxylation of glycerol withethylene oxide and/or propylene oxide is known per se, cf. the relevantspecialist literature.

Adducts of alkylene oxides with glycerol are generally known substanceswhich may be obtained by the relevant methods of preparative organicchemistry. On an industrial scale, they are produced by ethoxylation orpropoxylation of glycerol in the presence of basic catalysts, such asfor example lithium hydroxide, potassium hydroxide, sodium methylate,strontium phenolate or calcined hydrotalcite, at temperatures in therange from 120° to 180° C. and under pressures of 1 to 5 bar. If mixedalkoxylates are used, the alkoxylation reaction may take place in blocksor at random. After the alkoxylation reaction, the products may beneutralized by addition of acids (phosphoric acid, acetic acid, lacticacid). However, non-neutralized catalysts, especially lithium hydroxide,may also be used for the subsequent esterification step.

The esterification of the reaction product after the ethoxylation and/orpropoxylation of glycerol with the saturated or unsaturated C₆₋₂₄ fattyacids mentioned above is also carried out by methods known per se to theexpert (cf., for example, Synthetic fats by P. M. Williams in "Chemistryand Industry" (London) 19 1947), 253).

The process for the insertion of alkylene oxides, more especiallyethylene oxide and/or propylene oxide, is also described in detail inthe relevant specialist literature and is carried out in the presence ofcatalysts, such as in particular lithium hydroxide, calcinedhydrotalcite, potassium hydroxide or sodium alkoxylate, cf. EP-A-0 247509 where the insertion of alkylene oxides into triglycerides isdescribed in detail by further references to the prior art.

Accordingly, by inserting ethylene oxide and/or propylene oxide intonatural oils or fats, the pour point of the basic oils/fats can bedirectly reduced to a considerable extent. It is possible in this way toproduce inexpensive hydraulic base oils which have only to be slightlychemically modified in relation to the basic natural oils and fats inorder to be able to be significantly improved in regard to theirlow-temperature stability. However, a surprising feature in this regardis that the viscosity of the ethoxylated and/or propoxylated productshardly differs from that of the basic oils/fats and, in general, is evenincreased.

Since the processes for the production of the base oils according to theinvention are made up of individual process steps known per se, there isno need here for any further particulars.

The oils obtainable by the processes mentioned above may be used as baseoils for the formulation of hydraulic oils. These base oils showparticularly favorable low-temperature behavior because they arecharacterized by a particularly low pour point (titer). In addition,they are readily and rapidly biodegradable (CEC L33 T82 Test, ≧80%).

The present invention also relates to hydraulic oils containing the baseoils mentioned above in addition to the usual additives. The hydraulicoils according to the invention are obtainable by intensive mixing ofthe base oils with the usual additives. Suitable methods for thispurpose are known to the expert from the relevant literature.

The hydraulic oils according to the invention contain at least 90% byweight, preferably at least 95% by weight and, more preferably, at least98% by weight of one of the above-mentioned base oils or a mixturethereof.

The base oils according to the invention and, hence, the hydraulic oilcompositions containing them show high low-temperature stability so thatthere is no need to add additional pour point depressants or syntheticesters for typical applications. The base oils according to theinvention show a significantly reduced pour point in relation to thefats/oils on which they are based without any deterioration in theirviscosity in relation to that of the basic fats/oils.

To prepare the hydraulic oil from the base oil, other typical componentshave to be added in known manner. Thus, antioxidants, corrosioninhibitors, extreme-pressure additives, anti-wear additives or, wherenecessary, other pour point depressants may be added to the base oilsaccording to the invention.

The extreme-pressure additives are, in particular, sulfurizedtriglycerides, sulfurized fatty acid alkyl esters, sulfurized spermoils, phosphoric acid esters, such as trioleyl alcohol phosphate ortriaryl phosphate.

Particularly suitable anti-wear additives are zinc dialkyldithiophosphate compounds, such as zinc(di-2-ethylhexyldithiophosphate).

The products marketed as "Edenor" 2410 (by Henkel KGaA, D usseldorf) and"Viskoplex" (by R ohm, Darmstadt) are mentioned as examples of pourpoint depressants. These products are polymer-based pour pointdepressants which infinitely delay crystallization.

Suitable corrosion inhibitors are, in particular, succinic acidsemiesters, sorbitan monooleate, amine soaps of long-chain fatty acids.Additin (a product of Rheinchemie, Mannheim), Edenor or Eumulgin(products of Henkel KGaA, D usseldorf) are mentioned in this connection.

Suitable antioxidants are, in particular, combinations of stericallyhindered aromatic compounds, more particularly TBHQ (tert.butylhydroxyquinoline) or BHT (butoxylated hydroxytoluene), and anionicantioxidants, such as in particular, BHA (butoxylated hydroxyanisole) orphenothiazine (a product of Hoechst AG, Frankfurt). A liquidantioxidant--Edenor VP 2465 (a product of Henkel KGaA, Dusseldorf)--which consists of a combination of anionic and phenolicantioxidants may also be used.

Further information on the particular formulation of hydraulic oils,their additives and the quantities in which they are used can be foundin the prior art literature on this class of materials cited in detailin the foregoing.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES 1. Preparation of Glycerol Propoxylate Trioleate

a) Glycerol propoxylate

In a 4 liter steel autoclave, 0.45 g of lithium hydroxide was added to2400 g (26 moles) of glycerol. After heating to 80° C., adhering tracesof water were removed by evacuation and purging with nitrogen a total of5 times. The reaction mixture was then heated to 150° C., after which1500 g (26 moles) of propylene oxide were added in portions so that thepressure in the reactor did not exceed a value of 5 bar. On completionof the reaction (around 3 h), the mixture was cooled to 80° to 100° C.and a vacuum was applied for about 15 minutes to remove traces ofunreacted propylene oxide. Around 3900 g of glycerol propoxylate wereobtained in the form of a clear colorless liquid with a hydroxyl valueof 1200.

b) Glycerol propoxylate trioleate

A mixture of 157.2 g (1.04 mole) of glycerol propoxylate with an OHvalue of 1113 and 833.2 g (3 moles) of a technical oleic acid with anacid value of 203 and an iodine value of 90 was heated for 2 hours to240° C. in the presence of 1 g of tin oxalate. The water of condensationformed was distilled off. After heating for another 5 hours at 240° C.,the water of condensation was distilled off in a vacuum of 16 mbar. Inorder to complete esterification of the carboxylic acid, another 2.5 g(0.017 mole) of glycerol propoxylate with an OH value of 1113 was addedand the mixture was heated for 3 hours at 240° C. under a vacuum of 16mbar. The mixture was then cooled to 95° C., 20 g of bleaching earth(based on montmorillonite) were added and filtered off. The product wasdark yellow in color and slightly viscous. It had an OH value of 8.9 andan acid value of 0.9.

c) Reaction of rapeseed oil with propylene oxide (insertion)

In a 2 liter steel autoclave, 0.94 g of hydrated lithium hydroxide wasadded to a mixture of 872 g (1 mole) of rapeseed oil from new plants and8.7 g (95 mmoles) of glycerol, followed by heating to 100° C. Adheringtraces of water were removed by evacuation and purging with nitrogen atotal of 5 times. The reaction mixture was then heated to 180° C. and 58g (1 mole) of propylene oxide were added in portions so that thepressure in the reactor did not exceed a value of 5 bar. On completionof the reaction (approx. 3 h), the reaction mixture was cooled to80°-100° C. and a vacuum was applied for about 15 minutes to removetraces of unreacted propylene oxide. After neutralization of thecatalyst with 2.24 g of 90% lactic acid and filtration, a yellow liquidwas obtained in a quantity of around 930 g.

2. Comparison of Glycerol Monopropoxylate (GPO) Trioleate with RapeseedOil

1 Mole of glycerol is reacted with 1 mole of propylene oxide. Theglycerol monopropoxylate (GPO) formed was esterified with 3 moles of thefatty acid Edenor TiO5 (oleic acid from beef tallow). The product wascompared with rapeseed oil.

    ______________________________________                                                       GPO Trioleate                                                                           Rapeseed oil*)                                       ______________________________________                                        Acid value (DIN 53402)                                                                         2.4         1                                                Kinemat. viscosity                                                            (mm.sup.2) (DIN 51562)                                                        at 40° C.:                                                                              43.8        38.1                                             at 100° C.:                                                                             8.98        8.51                                             Viscosity index  192         210                                              (DIN ISO 2909)                                                                Demulsifying power [min.]:                                                                     >60         8                                                (DIN 51599)                                                                   Air separation capacity                                                                        7           6                                                (min.):                                                                       (DIN 51381)                                                                   Cloud point (°C.)                                                                       -21         -16                                              (DIN ISO 3015)                                                                Pour point (°C.)                                                                        -34         -17                                              ______________________________________                                         *)Refined rapeseed oil low in erucic acid                                

We claim:
 1. In a hydraulic oil comprising a base oil and at least oneof an antioxidant, corrosion inhibitor, extreme-pressure additive, oranti-wear additive, the improvement wherein the base oil compriseseithera) the product of the ethoxylation and/or propoxylation ofglycerol with from about 0.5 to about 3 moles of ethylene oxide and/orpropylene oxide and subsequent esterification with a saturated orunsaturated C₆₋₂₄ fatty acid, or mixtures thereof; or b) the product ofthe insertion of from about 0.5 to about 3 moles of EO and/or PO into anatural oil or fat other than castor oil.
 2. The hydraulic oil of claim1 wherein the base oil comprises product a).
 3. The hydraulic oil ofclaim 2 wherein the base oil consists of product a).
 4. The hydraulicoil of claim 1 wherein the base oil comprises product b).
 5. Thehydraulic oil of claim 4 wherein the base oil consists of product b). 6.The hydraulic oil of claim 1 wherein the base oil comprises at leastabout 90% by weight of the hydraulic oil.
 7. The hydraulic oil of claim6 wherein said quantity is at least about 95% by weight of the hydraulicoil.
 8. The hydraulic oil of claim 6 wherein said quantity is at leastabout 98% by weight of the hydraulic oil.
 9. The hydraulic oil of claim1 wherein in product a) from about 0.5 to about 2 moles of EO and/or POare used for the ethoxylation and/or propoxylation.
 10. The hydraulicoil of claim 1 wherein in product b) from about 0.5 to about 2 moles ofEO and/or PO are inserted into the natural oil or fat.
 11. The hydraulicoil of claim 1 wherein in product a) the saturated or unsaturated C₆₋₂₄fatty acid or mixture thereof is at least one of caproic acid, caprylicacid, capric acid, lauric acid, myristic acid, palmitic acid, stearicacid, arachic acid, behenic acid, lignoceric acid, myristoleic acid,palmitoleic acid, oleic acid, gadoleic acid, erucic acid, ricinoleicacid, linoleic acid, linolenic acid, arachidonic acid or clupanodonicacid.
 12. The hydraulic oil of claim 1 wherein in product b) the naturalfat or oil is coconut oil, palm kernel oil, palm oil, peanut oil, cottonoil, soybean oil, sunflower oil, rapeseed oil rich or poor in erucicacid, tallow, or fish oil.
 13. The hydraulic oil of claim 1 wherein inproduct a) from about 0.5 to about 1 mole of EO and/or PO are used forthe ethoxylation and/or propoxylation.
 14. The hydraulic oil of claim 1wherein in product b) from about 0.5 to about 1 mole of EO and/or PO areinserted into the natural fat or oil.
 15. The hydraulic oil of claim 1wherein in product a) the C₆₋₂₄ fatty acid is a mixture of fatty acidsobtained from a natural source.
 16. The hydraulic oil of claim 1 whichis free from pour point depressants.